08 outback won't idle

[oh8ootback]

Greetings.  I have an 08 Outback 5mt 164k.  Recently started dieing at idle.  It's fine when in the cold start cycle but will not stay at idle when fully up to temp.  Previous owner complained of this when I bought it.  I've driven it 15k and this is the first I've experienced it.  Previous owner had a new long block installed.  I mostly only drive it in the winter for skiing and ski trips.  I noticed this winter when it was cold (below 15f) the car never would get to full temp and would lose temp at idle...like the thermostat is stuck open.  I'm now wondering if that's why I never had a problem because it would be in the cold start cycle the whole time?  I dunno.  It's probably going to be hard to diagnose as it won't stay running unless you hold the revs over 1k.  Any ideas?  TIA.

[xt2005bonbon]

Is this a turbo outback?

Have you checked for vacuum leaks?

[oh8ootback]

NA 2.5 base.  I have not checked for vacuum leaks...not sure how to go about that.  I was going to try a known good maf, clean the tb, and do the idle relearn when it cools off this wxend.  

[KZJonny]

Cold start would be running rich correct? Until the engine warms up….

If it never gets to temp, then perhaps the obvious thermostat would be a good thing to investigate as well. They fail, or cheap aftermarket are not well liked. OEM or (some other specific manufacturer, Gates?) seem to be preferred.

Perhaps a fuel treatment is in order? Clogged injectors not delivering enough fuel when at warm idle?

No CEL’s to help diagnose?

Only time I had really poor idle on my 2.5i was when I forgot to reconnect the MAF sensor after having all the intake apart.

[oh8ootback]

Nope no cel.  Which seems odd to me.  It reaches temp...it was just doing that in very cold weather.  I'll report back after the new maf, tb clean, and idle relearn.  It may have to go to the local suby guru beyond that.  I guess could be front o2, egr, or intake manifold/gasket leak.  

[xt2005bonbon]

You need a way to look at the ECU parameters, something like the BtSsm app so you can see what your fuel trims are. That would be very helpful.

[oh8ootback]

I agree that would tell the story.  What a cool app!  I did notice when checking for stored codes the obd port seems to have a loose connection as I had to fiddle with it and hold it to get the scanner to work.  Coulda been oreillys scanner too.  Would a loose port cause there to be no cel/stored info?  The good news is I work from home and don't really need the car daily.  I appreciate all the replies!  Thanks.

Edited June 7, 2023 by oh8ootback

[xt2005bonbon]

I don't think a loose port would cause no cel info. Are you sure the port is loose? It could just be that the port is not securely affixed on that lower panel. Have a closer look.

[Febreze Mee]

I'm willing to bet it's a vacuum leak somewhere. Either internal or external. Does the car have a known misfire?

You can check for a vacuum leak by hooking up a smoke machine to any one of the ports and allowing it to fill your intake. Watch for any unwarranted seepage.  

[oh8ootback]

A known misfire?  I don't know that it has a misfire so I guess not.  Today I put a new maf, air filter, cleaned tb, and did the idle relearn.  Went on a drive and right when I was ready to declare it fixed, it started doing it again.  However I think I learned something new.  It is totally related to engine temp.  It's cooler today...70f.  Where do y'all think the temp gauge should read?  When I'm out on country roads and the gauge is a hair below half it idles fine.  When I get in town the temp gauge goes to half...perfectly horizontal.  There's a slight shudder when the fan kicks on and it starts misbehaving.  So it started dieing in town.  I got back out on open roads, the temp gauge went back to below half, and it idled fine.  Does that still seem vacuum related?  Very strange. 

[Febreze Mee]

No, not anymore. Time to investigate the thermostat. 

[KZJonny]

Or maybe voltage? If the fan kicking in is causing problems, there is a slim chance that battery is on the way out or perhaps the alternator is only making *just* enough to keep thing going.

Easy to look for dirty/corroded/missing grounds (ground straps?) Quick check to see battery voltage and charging volts?

Could sort of explain why highway driving would be okay, but too much stop and go and it dies?

Pulling at straws a little, but if the thermostat doesn't check out. I've been burned by chasing ghosts a few times, when it was all just a low charge on the battery, or need of a new one.... I check battery condition and charging before pretty much all jobs now, just in case. Doing a load test never hurt either.

Edited June 9, 2023 by KZJonny

[kzr750r1]

Circling wayyyy back... May want to check if the gaskets under the manifold are updated. Not sure 100% about the 08 but the earlier MY had an updated set in later years.

There were complaints of Vac leak due to these gaskets getting hard and not creating a seal any more. New units were taller and squared off as opposed to a chamfer edge on the sealing surface.